Production of ethylbenzene



Oct. 22, 1946'.-

` L. SCHMERLING PRODUCTION OF ETHYLBENZENE Filed July 24, 1942 NIN.

Patented Oct. 22, W1946 UNITED NSTATES, PATENT OFFICE 2,409,802PRODUCTION F ETHYLBENZENE Louis Schmerling, Chicag versal `Oil ProductsCompany,

o, Ill., assignor to Uni- Chicago, Ill., a

corporation of Delaware Application July 24, 1942, Serial No. 452,250

2 Claims. l

This is a continuation-in-part of my copending application Serial No.386,110, filed March 31, 1941.

This invention relates particularly to the production ofmonoethylbenzene by the interaction of speciiic reactants in thepresence of specific catalysts and under specific operating conditions.

The invention is characterized by lthe use of benzene as one reactant,ethyl alcohol as the other reactant, phosphoric acid as the catalyst,and specific temperature and pressure conditions of operation. Inaddition, the present invention discloses a number of other featureswhich will hereinafter be set forth in detail.

It has heretofore been suggested that aromatic hydrocarbons may bereacted with alcohols in the presence of acid type catalysts to producealkylated aromatics. British Patent No. 464,752 teaches that aromaticcompounds may be reacted with compounds yielding olenic hydrocarbons ondehydration, such as ethers or alcohols, in the presence of phosphoricacid catalysts, but this patent, as well as the other priol` art, doesnot definitely teach the reaction of ethyl alcohol with benzene in thepresence of phosphoric acid catalysts.

Since prevision inr chemical reactions cannot in all cases be made withaccuracy, it cannot be definitely stated in advance that the reaction ofethyl alcohol and benzene will occur under the conditions specified inthe reference heretofore mentioned For example, when usingV sulfuricacid as the catalyst, aromatic hydrocarbons may be readily alkylatedwith p-ropyl and butyl alcohols buty to the best of my knowledge,aromatic 4hydrocarbons cannot satisfactorily be reacted with ethylalcohol inthe presence of sulfuric acid catalyst under any conditions ofoperation so far determined.

VIn addition, the present invention discloses the feature of utilizingan excess of benzene in the reaction zone. This operation has a numberof advantages, the primary ones being (1) conducting the reactions undersubstantially adiabatic conditions and (2) dissolving the unconvertedethylene in the benzene for recycling. These and other advantages ofthis particular method of operation will hereinafter be described indetail.

It is believed that, in the reaction of ethyl alcohol with benzene toproduce ethylbenzene, the ethyl alcohol is first dehydrated under theconditions of operation to yield Water and ethylene, and that thebenzene is then alkylated by the ethylene to produce ethylbenzene. Aparticular advantage in the use of ethyl alcohol as one of the reactantsis that the dehydration reaction is endothermic and absorbs heat, whilethe alkylation reaction is, exothermic and liberates heat. Thus, theheat liberated by the exothermic alkylation reaction is utilized in theendothermic dehydration reaction, and this effects an efiicient thermalsystem and, at the same time, aids in permitting the process of theinvention to be effected under substantially adiabatic conditions.

As another particular feature, 1 have found that, when operatingaccording to the teachings of the present invention, the nal products ofthe process are substantially the desired monoethylbenzene, and that theproduction of diethylbenzene is substantially avoided. Some undesiredhigher boiling poly-alkylated aromatics are also produced during thereaction, but these higher boiling products are kept at a minimum, aswill be hereinafter shown in the example.

1n one specific embodiment the present invention relates to a processfor producing monoethylbenzene which comprise contacting benzene withethyl alcohol in the presence of an acid of phosphorus at a temperaturebetween about 500 F. and about 750 F. under a pressure of between about200 pounds and about 1200 pounds per square inch.

The ethyl alcohol utilized in thepresent process may be obtained fromany convenient source. 1t need not be oi 100% purity and may containother compounds in admixture therewith. The ethyl alcohol fractionshould not contain propyl alcohol or other higher boiling alcohols orpropylene or other higher boiling olefinic hydrocarbons, since thesealcohols or olenic hy-drocarbons readily react with benzene and thuswill produce higher boiling alkylated products which are not desired inthe present operation. It is understood, however, that the resultsobtained by utilizing different composition ethylene fractions are notnecessarily equivalent and that more efficient operation is obtained byutilizing ethyl alcohol fractions of higher purity.

Likewise, the benzene utilized in the present invention may be obtainedfrom any convenient source. The benzene used need not be of purity butmay contain other compounds in admixture therewith. The results obtainedby different composition benzene-containing fractions are notnecessarily equivalent.` More efficient operation is obtained byutilizing benzenecontaining fractions which are not contaminated withtoo great quantities of other compounds.

The essential ingredient of the catalyst which is .employed in the.present invention is `phosphoric acid, which may constitute 80% or moreof the catalyst mixture and in `most cases is over 30% by weightthereof. Of the various acids of phosphorus, orthoor pyro-phosphoricacids are generally preferred on account of their ethylating abilities,their cheapness, and the readiness with which they may be procured,although the invention is not restricted to their use but may employ anyof the other acids of phosphorus insofar as they are adaptable. It isnot intended to infer, however, that the different acids of phosphoruswhich may be employed will produce identical effects upon any givenreaction as each acid will exert its own characteristic action.Y Theactivity of a given` catalyst is also dependent upon the ratio of acidto siliceous adsorbent contained therein.

Solid phosphoric acid catalysts, which are particularly utilizable inthe present process, may be made by mixing an acid of phosphorus, suchas orthoor pyrophosphon'c acid, with a finely divided, relatively inertand a generally silioeous carrier such as, for example, kieselguhr, toform a rather wet paste (the acid ordinarily being in major proportionby weight); calcining attemperatures in the order of 750 to 950 F. toproduce a solid cake; grinding and sizing to produce particles of usablemesh; and rehydrating the catalyst granules at temperatures of the orderc-f 500 F. to produce an acid composition corresponding to the optimumethylating activity which usually corresponds. approximately to thepyro-acid in composition.

This catalyst preparation procedure may be varied by forming lparticlesfrom the original paste by extrusion or pelleting methods and followingwith the caloining and rehydrating steps.

In the reactions taking place during calcination it is evident that someacid is fixed on the carrier and that some metaphosphoric acid, which issubstantially without ethylating activity, is formed. The rehydratingstep evidently produces an acid composition corresponding closely to thepyro-acid having a formula H4P2O7. Unless rehydratio-n is practiced thetemperature of approximately 575 F. should not be exceeded in thecalcination step. And if higher temperatures produce catalyst particlesof greater structural strength, depending upon the character of thecarrier' and the composition 'of lacid fixed therewith, the compositionof the acid may be brought tothe desired point by contact withsuperheated steam at approximately 500 F. at atmospheric pressure. Thisbrief description oi a solid phosphoric acid catalyst and of itspreparation is not exhaustive, as both have been generally describedalready inV United States Patents Nos. 1,993,512 and 1,993,513 andothers.

` Solid phosphoric acid catalyst are hygroscopic toV avaliable extentand areV best ground, sized, and'preserved for use out of contact withmoist air.

As to the conditions of operation which should be employed in thepresent invention, the temperature should not be below about 500 F. andshould not be above about 750 F. and preferably should be within therange of from about 525 to about 675 F. When utilizing temperaturesbelow.500 F. the reaction proceeds very slowly andrequires the use ofexceptionally long times of contact, which are impractical from acommercial viewpoint. At temperatures above '750g F., difliculty isencountered due to the formation of carbon, and. the productionof con- 4siderable amounts of undesired higher and lower boiling products.

The pressure employed should be within the range of about 200 to about1200 pounds per square inch, and preferably within therange of about 250to 900 pounds per square inch. The use of the pressures specifiedhereinA serves several denite purposes, including dissolving theunreacted ethylene in the benzene, which operation greatly facilitatesthe recycling of the benzene and ethylene to the reaction zone forfurther conversion therein. In addition higher yields of the desiredmono-ethylbenzene are obtained by the use of the pressures specifiedthan by the useof either higher or lower pressures.

As heretofore mentioned, the ethyl alcohol probably undergoesdehydration to Water and ethylene. I have found that substantiallycomplete dehydration of the ethyl alcohol is effected under theconditions of operation and that'the products from the reaction zone donot contain ethyl alcohol. However, the products may contain someethylene which has not reactedwith the benzene and, as a `particularfeature'of 'the present invention, the unreacted ethylene is dissolvedin the benzene `and recycled to the reaction zone for further conversiontherein. The molal ratio of benzene, including both the benzeneintroduced from an outside source and the recycled benzene, to thealcohol introduced from an outside source and the recycled ethyleneshould be'within the range of about 2:1 to about 20:1, and preferablywithin the range of about 4:1 to about 15:1. rlhe inolal ratio of thebenzene to ethyl alcohol and recycled ethylene should not be less thanabout 2:3., since the benefits of the present invention are not obtainedwith such low proportions of benzene to ethylene. On the other hand, theuse of molal ratiosof benzene to ethyl alcohol and recycled ethylene inexcess of 20:1 are unnecessary since they produce no further beneficialeffects and instead only increase the size and cost of plant equipmentbeyond practical proportions.

The Vtime of cont-act `to be employed will be correlated with theparticular temperature and pressure utilized in vany given operation toproduce the desired results.

In effecting the reaction between the benzene and ethyl alcohol,according to the present invention, the exact method of procedure varieswith the composition and activity of the catalyst employed. A simpleprocedure consists in contacting a mixture of benzene and ethyl alcoholwith the catalyst at the desired temperature and pressure` In case thecatalystl is employed in either liquid or nely divided condition, batchor continuous. operations may be effected byV utilizing an efficientstirring mechanism to insure intimate contact of the reactantandcatalyst.l In other types of operation the reactants may be mixedl withnely divided or'powdered catalysts and reacted Vin a substantiallyflu-id. type of operation.

A particularly preferred method ofV operation is to dispose the catalystin solid condition in a reaction zone and pass the proper proportionsofbenzene, ethyl alcohol and recycled ethylene over the catalyst under thedesired` temperature and pressure conditions. If desired-.the ethylalcohol and/cr recycled ethylene-benezene fractions may be introduced atintermediate points in thereaction zone. y Y, ,l The products from'thereaction zone will com.- Drise ,essentiallyy mono-ethylbenzene, higherboil.-

in g alkylated aromatics, excess benzene, and unreacted ethylene. Theseproducts may be introduced to one or more fractionating or separatingzones whereby the desired mono-ethylbenzene is separated and recovered.Likewise, the higher boiling aromatics may be separated and recovered.The excess benzene and unreacted ethylene are usually withdrawn as anoverhead product of the fractionating Zone and are condensed underconditions to dissolve substantially all of the unreacted ethylene inthe benzene. The exact temperature of cooling to be employed will dependupon the excess of benzene, amount of ethylene and the pressureutilized. In general, cooling of these products to substantiallyatmospheric temperature or slightly lower will be sufficient to dissolvethe ethylene in the benzene under the high pressure and with the excessof benzene heretofore specified. This fraction may then be readilypumped back to the reaction zone for further conversion therein. In thismethod of operation the use of compressors or other expensive equipmentto recycle the ethylene is eliminated. This method of operation isparticularly important from a commercial viewpoint.

The commercially important operation above referred to will now bedescribed in connection with the accompanying drawing which is adiagrammatic illustration of the process and apparatus elements employedtherein.

Referring more particularly to the drawing, benzene and ethyl alcoholare charged through line I, containing valve 2, and commingled with arecycle stream of benzene containing dissolved ethylene. produced ashereinafter described, and

the mixture charged to reactor 3 containing solid phosphoric acidcatalyst. In the reactor, the ethyl alcohol is converted to ethylene andwater and the benzene is alkylated with the ethylene. The reactionproducts, which comprise essentially monoethylloenzene,polyethylbenzenes, excess benzene and unreacted ethylene, are removedfrom the reactor through line 4, containing valve 5, and are passed intofractional distillation means 9. The unreacted benzene and ethylene arewithdrawn as an overhead vapor from fractionating means 6 through line1, containing valve 8, and are passed into condenser 9 where they arecondensed under conditions such that substantially all of the ethyleneis dissolved in the benzene. The eilluent from condenser 9 ispassed intoreceiver I0 from which it is withdrawn through line II, containing pumpI2. Part of the discharge of the pump is directed through line I3,containing valve I 4, and enters near the top of fractionator 6 where itserves as reflux. Another portion is recycled through line I5,containing valve I6, to reactor 3. The bottoms product from fractionator6, which comprises mono and polyethylbenzenes, is withdrawn through lineII, containing valve I8, and is charged to fractionator I 9. An overheadproduct, consisting of monoethylbenzene, is withdrawn from fractlonatorI9 through line 20, containing valve 2|. A bottoms product, comprisingpolyethylbenzenes, is withdrawn through line 22, containing Valve 23.

The following example of one operation is given for the purpose offurther illustrating the invention, but not with the intention of undulylimiting the same.

'75 cc. of benzene and 4 cc. of ethyl alcohol per hour were passedthrough 40 cc. of Ill-|12 mesh solid phosphoric acid catalyst maintainedat 662 F. under a pressure of 600 pounds per square inch. 4.8 grams perhour of monoethylbenzene and 0.3 gram of more highly alkylated benzeneswere produced. After four hours of operation, the carbon on the catalystamounted to 0.38% by weight of the catalyst. The exit gas amounted to anaverage of 0.02 cubic feet per hour. The exit gas at the beginning ofthe experiment consisted chiefly of nitrogen, which nitrogen wasoriginally introduced to pressure the unit, and later presumablyconsisted mostly of ethylene, although in this particular experiment thequantity of liberated ethylene was not measured. Water was recovered inadmixture with the alkylated products but, in this particularexperiment, the amount of water was not measured.

I claim as my invention:

l.. A process for the production of monoethylbenzene which comprisesreacting benzene, ethyl alcohol and ethylene at a temperature of fromabout 500 F. to about 750 F. under a pressure of from about 200 poundsto about 1200 pounds per square inch in the presence of a solidprosphoric acid catlayst in a reaction zone, said reaction comprisingdehydration of the ethyl alcoho1 to Water and ethylene and alkylation ofthe benzene by ethylene, separating the reaction products into alkylatedbenzene and unreacted ethylene and benzene, recovering said alkylatedbenzene, cooling said unreacted ethylene and benzene under a pressure offrom about 200 pounds to about 1200 pounds per square inch in order todissolve said unreacted ethylene :in said benzene, recycling saidbenzene and dissolved ethylene to the reaction zone for furtherconversion therein, and maintaining in said reaction zone from 2 to 2Omolecular proportions of benzene to one molecular proportion of ethylalcohol and ethylene. l

2. A process for the production of monoethylbenzene which comprisesreacting benzene, ethyl alcohol and ethylene at a temperature of about525 F. to about 675 F. under a pressure of from about 250 pounds toabout 900 pounds per square inch in the presence of a solid phosphoricacid catalyst in a reaction zone, said reaction comprising dehydrationof the ethyl alcohol to vWater and ethylene and alkylation of thebenzene by ethylene, separating the reaction products into alkylatedbenzene and unreacted ethylene and benzene, recovering said alkylatedbenzene, cooling said unreacted ethylene and benzene under a pressure offrom about 250 pounds to about 900 pounds per square inch in order todissolve said unreacted ethylene in said benzene, recycling said benzeneand dissolved ethylene to the reaction zone for further conversiontherein, and maintaining in said reaction zone from 4 to 16 molecularproportions of benzene to one molecular proportion of ethyl alcohol andethylene.

LOUIS SCHMERLING.

